Springer-Verlag Berlin Heidelberg 1988. It is commonplace to base computer security and information security on hard problems. Recent cryptosystems have been based on the knapsack problem [DE83, pp. 118-126; BRS5] and the problem of factoring an integer [DE83, pp. 104-1091. The former problem is N P complete [GA79, p. 2471. The place of the latter problem in complexity theory is not well understood, but it has been around in number theory for a long time.
